The present invention relates to a positive-working, photosensitive mixture of an ester or an amide of a 1,2-naphthoquinonediazide sulfonic or carboxylic acid as the photosensitive compound, a phenolic resin which is soluble in aqueous alkaline solutions and insoluble in water as the binder, and a speed enhancer. The invention also relates to a photosensitive recording material which is produced from a layer support and a layer comprising the photosensitive mixture, and to the use of this material.
Photosensitive compositions or recording materials, respectively, the imagewise-exposed areas of which become soluble in a developer solution and the unexposed areas of which remain insoluble have been known for a long time. For the preparation of such materials, layers which contain o-quinonediazides as photosensitive compounds and which contain resins with groups providing alkali solubility, for example phenolic resins, as binders are primarily used in practice.
Copying layers of this type have, however, a relatively unsatisfactory photospeed. Therefore, various attempts have been made to improve the photospeed of radiation-sensitive materials based on an o-quinonediazide compound and an alkali-soluble phenolic resin. The photospeed of the recording layer can be enhanced, for example, by reducing the amount of alkali-soluble phenolic resin or by increasing the amount of o-quinonediazide compound. It is a disadvantage of these proposed improvements that the required resistance to overdevelopment of the material and the development range, i.e., the time available for an optimum development, are reduced. Therefore, measures of this kind cause problems in practical use.
By combining o-quinonediazide compounds with phenolic resins possessing increased solubility in aqueous-alkaline developers, the photospeed can be apparently increased, but here, too, the resistance to overdevelopment decreases and the development range gets too short for practical purposes.
There have also been attempts to improve the photospeed by incorporating special sensitizers into the photosensitive mixture.
U.S. Pat. No. 3,661,582 teaches the addition of certain heterocyclic compounds, such as 2-azacyclononan-2-one, indole, quinazoline or tetrazole, to mixtures containing o-naphthoquinonediazides, in order to improve the photospeed of the mixtures. In this case, too, an extremely narrow development range results.
Japanese Patent Application No. 42 449/1971 describes various additives, for example, triphenylmethane dyes, benzaldehyde-m-tolylhydrazone, halogenated hydrocarbons and azo dyes, that are intended to improve the photographic sensitivity; however, none of these compounds has a significant effect.
In German Offenlegungsschrift No. 26 57 922, equivalent to U.S. Pat. No. 4,115,128, the addition of cyclic acid anhydrides is disclosed for the same purpose as above. Here, too, increased photospeed can only be achieved at the expense of reduced resistance to overdevelopment. Similar results are obtained when gallic acid is added to the recording layer to increase the photospeed, in accordance with German Offenlegungsschrift No. 32 01 151.
German Offenlegungsschrift No. 28 47 878, equivalent to U.S. Pat. No. 4,275,139, describes the addition of a condensation product obtained from formaldehyde and a hydroxybenzophenone to a photosensitive mixture, in order to increase the photospeed. It is true that the photospeed is considerably increased by the addition of this type of polycondensation products, where the hydroxybenzophenone molecules are mutually linked via methylene bridges and at least one OH-group must be adjacent to the carbon atom carrying the carbonyl group, but it is a disadvantage that either relatively large amounts of the admixture are required or the resistance to chemicals of the printing stencil is reduced. It has also been found that in the presence of the condensation product obtained from 2,3,4-trihydroxybenzophenone and formaldehyde the resulting photospeed strongly depends on the type of development chosen. If development is, for example, performed by immersion in a developer bath, the resulting photospeed, measured by means of a continuous-tone test wedge, is considerably higher than in those cases where development is performed manually.